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US 2020/0051709A1 Feb.13,2020 6 chemicalspeciesorfunctionalgroupsintheinterstitial basedonthenotionthattheinter-grapheneplaneseparation spacesbetwengrapheneplanesservestoincreasethe hasbenincreasedfrom0.354nminnaturalgraphiteto inter-graphenespacing(202,asdeterminedbyX-raydif 0.6-1.1nminhighlyoxidizedgraphiteoxide,significantly fraction),therebysignificantlyreducingthevanderWals weakeningthevanderWalsforcesthatholdneighboring forcesthatotherwiseholdgrapheneplanestogetheralong planestogether.Ultrasonicpowercanbesuficientofurther thecrystalographicc-axisdirection.TheGICorGOismost separategrapheneplaneshetstoformseparated,isolated, oftenproducedbyimersingnaturalgraphitepowder(20in ordiscretegrapheneoxide(GO)shets.Thesegraphene FIGS.1(a)and10inFIG.1(6)inamixtureofsulfuric oxideshetscanthenbechemicalyorthermalyreducedto acid,nitricacid(anoxidizingagent),andanotheroxidizing obtain“reducedgrapheneoxides”(RGO)typicalyhaving agent(e.g.potasiumpermanganateorsodiumperchlorate). anoxygencontentof0.01%-10%byweight,moretypicaly TheresultingGIC(22or102)isactualysometypeof 0.01%-5%byweight,andmosttypicaly0.01%-2.0%by graphiteoxide(GO)particles.Strongoxidationofgraphite weightofoxygenwithheavychemicalreductionusinga particlescanresultintheformationofagel-likestatecaled “GO gel”21.TheGIC2isthenrepeatedlywashedand rinsed inwater to remove exces acids,resulting in a graphite oxide suspension or dispersion,which contains discreteandvisualydiscerniblegraphiteoxideparticles dispersedinwater.Therearetwoprocesingroutestofolow afterthisrinsingstep: reducingagentlikehydrazine. [074] Itisimportanttofurtheremphasizethefactthat,in thetypicalpriorartproceses,ultrasonificationisusedafter intercalationandoxidationofgraphite(i.e.,afterfirstexpan sion)andmosttypicalyafterthermalshockexposureofthe resultingGIC orGO (i.e.,aftersecondexpansionorexfo liation)toaidinbreakingupthosegraphiteworms.There [0069]Route1involvesremovingwaterfromthesuspen arealreadymuchlargerspacingsbetwenflakesafterinter siontoobtain“expandablegraphite,”whichisesentialya masofdriedGICordriedgraphiteoxideparticles.Upon exposureofexpandablegraphitetoatemperatureinthe calationand/orafterexfoliation(hence,makingitposible toeasilyseparateflakesbyultrasonicwaves).Thisultra sonicationwasnotperceivedtobecapableofseparating rangefromtypicaly80-1,050°C.foraproximately30 thoseun-intercalated/un-oxidizedlayerswheretheinter secondsto2minutes,theGICundergoesarapidexpansion graphenespacingremains<0.34nmandthevanderWaals byafactorof30-30toform“graphiteworms"(24or104), forcesremainstrong. whichareeachacolectionofexfoliated,butlargelyun separatedgraphiteflakesthatremaininterconected. [0070] In Route 1A, these graphite worms (exfoliated graphite or “networks of interconected/non-separated graphiteflakes”)canbere-compresedtoobtainflexible graphiteshetsorfoils(26or106)thattypicalyhavea thicknesintherangefrom0.1mm (10um)-0.5mm (500 um).Alternatively,onemaychosetousealow-intensityair milorshearingmachinetosimplybreakupthegraphite wormsforthepurposeofproducingtheso-caled“expanded graphiteflakes”(49or108)which containmostlygraphite [075] Theaplicant'sresearchgroupwastheveryfirstin theworldtosurprisinglyobservethat,underpropercondi tions(e.g.,withanultrasonicfrequencyandintensityand undertheasistanceofacertaintypeofsurfactant),ultra sonication can be used to produce ultra-thin graphene directlyfromgraphite,withouthavingtogothroughchemi calintercalationoroxidation.Thisdisclosurewasreported in apatentaplication [A.Zhamu,etal.,“Method of ProducingExfoliatedGraphite,FlexibleGraphite,andNano GraphenePlates,"U.S.patentSer.No.1/80,728(May8, 2007);now U.S.Pat.No.7,824,651(Nov.2,2010)].This flakesorplateletsthickerthan10nm(hence,notanano "directultrasonication"procesiscapableofproducingboth materialbydefinition). single-layerandfew-layerpristinegrapheneshets.This [0071]Exfoliatedgraphiteworms,expandedgraphite inovativeprocesinvolvessimplydispersingpristine flakes,andtherecompresedmassofgraphiteworms(com graphitepowderparticles20inaliquidmedium(e.g.,water, monlyreferedtoasflexiblegraphiteshetorflexible alcohol,oracetone)containingadispersingagentorsur graphitefoil)areal3-Dgraphiticmaterialsthatarefunda factanttoobtainasuspension.Thesuspensionisthen mentalydiferentandpatentlydistinctfromeitherthe1-D subjectedtoanultrasonicationtreatment,typicalyata nanocarbonmaterial(CNTorCNF)orthe2-Dnanocarbon temperaturebetween0°C.and10°C.for10-120minutes, material(grapheneshetsorplatelets,NGPs).Flexible resultinginultra-thinpristinegrapheneshetssuspendedin graphite(FG)foilsandaltheexpandedgraphitefilmsare aliquidmedium.Theresultingsuspensioncanbecastto totalydarkandopaque,notsuitableforuseasatransparent formapristinegraphenefilm38.Nochemicalintercalation conductiveelectrode. oroxidationisrequired.Thegraphitematerialhasnever [0072]InRoute1B,theexfoliatedgraphiteissubjectedto been posedtoanyobnoxiouschemical.Thisproces high-intensitymechanicalshearing(e.g.usinganultrasoni combinesexpansion,exfoliation,andseparationintoone cator,high-shearmixer,high-intensityairjetmil,orhigh step.Hence,thissimpleyetelegantmethodobviatesthe energybalmil)toformseparatedsingle-layerandmulti nedtoexposegraphitetoahigh-temperature,orchemical layergrapheneshets(colectivelycaledNGPs,33or12), oxidizingenvironment.Upondrying,theresultingNGPsare asdisclosedinourU.S.aplicationSer.No.10/858,814. esentialypristinegraphene,containingnooxygenandno Single-layergraphenecanbeasthinas0.34nm,while surfacedefects.Thesepristinegrapheneshets,single-layer multi-layergraphenecanhaveathicknesupto10nm.In thepresentaplication,thethicknesofmulti-layerNGPsis typicalylesthan 20nm.TheNGPs (stilcontaining oxygen)maybedispersedinaliquidmediumandcastinto aGO thin film 34. [0073]Route2entailsultrasonicatingthegraphiteoxide orhigher(ifhigherfrequency)pereachsuspendedgraphite suspensionforthepurposeofseparating/isolatingindividual particle.TheresultingNGPsarepristinegraphene,being grapheneoxideshetsfromgraphiteoxideparticles.Thisis single-grainorsingle-crystalineandwithoutanyintention ormulti-layer,arealhighlyconductivebothelectricalyand thermaly. [076] Thisdirectultrasonicationprocesmaybeconsid eredaspelingofgraphenelayersatarateof20,0 atemptspersecond(iftheultrasonicfrequencyis20kHz)PDF Image | HIGHLY CONDUCTING AND TRANSPARENT FILM AND PROCESS
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